Liquid bleaching agents generating active oxygen such as hydrogen peroxide or solid bleaching agents such as persalts such as sodium perborate, decompose at a fast enough rate to be compatible with a bleaching process only at temperatures above 60.degree. C.
Household washing powders at moderate temperature are a currect topic linked to the problem of energy savings. Further, use in a washing machine of an effective bleaching process at a temperature below 60.degree. C. offers certain advantages. In the case of cotton fabrics less degradation of the cellulose is noted and consequently there is a reduction in the wear of clothes. An improved bleaching is observed in synthetic fabrics or textile articles treated with a sizing agent assuring their crease resistance and permanent pressing and which cannot support a temperature above 60.degree. C. Bleaching at moderate temperature reduces the risk of attack of the dyes or their transfer from one fabric to the other. This type of bleaching also promotes the fight against pollution by lowering the polyphosphate content of the waste waters.
There is known from U.S. Pat. No. 4,025,453 a process of activating a peroxide base bleaching agent in which have been incorporated in an aqueous medium: (a) a peroxide base bleaching agent, (b) cyanamide and/or a metallic cyanamide in an amount suitable for activating the peroxide, and, optionally (c) a Group II A metal compound. The aqueous medium is kept in an alkaline state, optionally by incorporating a buffer therein, provided that if constituent (b) is cyanamide and if constituent (c) is absent, the aqueous medium is kept at a pH greater than 7.5.
However, it has been found that bleaching in the presence of a cyanamide type activator causes a certain depolymerization of textile polymers and particularly cellulose fibers.
The degradation observed is particularly pronounced when the washing temperature exceeds 60.degree. C., and especially when it reaches 90.degree. C.; a 90.degree. C. temperature is a relatively frequent case when an all-temperature washing powder is involved. At 90.degree. C., depolymerization is such that it causes a degradation that can hasten the wear of cotton clothing during successive washings.
On the other hand, although the prior teaching has proposed ethylenediaminetetraaceticdimagnesium compound as constituent (c) of the activating composition, it has been observed that this adjuvant, under prescribed use conditions, has practically no effect on the degradation observed in cellulose fibers.